C1-inactivator-resistant fibrinolytic activity in plasma euglobulin fractions: its relation to vascular activator in blood and its role in euglobulin fibrinolysis.

Abstract

Addition of Cl-inactivator to plasma euglobulin fractions revealed that part of their fibrinolytic activity is resistant to this inhibitor, while another part is inactivated. The resistant part of the activity fluctuates in parallel with changes in blood fibrinolytic activity caused by diurnal fluctuations, stress or venous occlusion. Purified plasminogen activators of extrinsic origin (human tissue activator and vascular perfusion activator) were found to be resistant to Cl-inactivator. The resistant part of the euglobulin activity therefore seems to indicate the presence of fluctuating amounts of a plasminogen activator of extrinsic origin in plasma. Optimal recovery of the resistant activity from plasma was achieved in euglobulin fractions prepared at pH 5.9 with a plasma dilution 1:10, in which resistant activity could be quantitatively assayed. Samples of morning plasma with baseline levels of fibrinolytic activity have levels of resistant activity amounting to only a few blood activator units (BAU)/ml. Samples of afternoon plasma showed a moderate increase in the resistant activity, while plasma collected after venous occlusion of the arm showed an enormous increase to 138 ± 29 (SD) BAU/ml (n=7). The Cl-inactivator susceptible activity can be optimally recovered by isoelectric precipitation in the presence of dextran sulphate. It seems to originate from intrinsic proactivator systems. It was demonstrated that extrinsic activator has the capacity to enhance the generation of activator activity in these intrinsic systems in vitro.